Tube and pole piece assembly for circuit breakers



.Sept. 26, 1967 A. R. NORDEN TUBE AND POLE PIECE ASSEMBLY FOR CIRCUIT BREAKERS Filed July 23, 1965 1 0 CONNECTING MUM; OF

THE CIRCUIT will.

vtralnnvvlitrnilllflilli 1il/ 1 l l lmg |NVENTOR Mam/v05 war BY Wm ATTORNEY} United States Patent 3,344,376 TUBE AND POLE PIECE ASSEMBLY FOR CIRCUIT BREAKERS Alexander R. Norden, New York, N.Y., assignor to Murray Manufacturing Corporation, a corporation of New York Filed July 23, 1965, Ser. No. 474,392 4 Claims. (Cl. 335240) ABSTRAKIT OF THE DISCLOSURE This invention relates to an improved tube and pole piece assembly, and, in particular, to a hydraulic-magnetic time delay tube for use in magnetically operable circuit breakers.

The tube and pole piece assembly as utilized in a circuit breaker of the type disclosed in the United States Patent No. 2,890,306 comprises generally a hermetically sealed non-magnetic tube closed at one end by a pole piece; i.e. a magnetic member. Contained within the tube are a movable pole piece or core and a spring for retarding the movement of the movable core towards the stationary pole piece. The tube is also preferably filled with a liquid to dampen further the movements of the pole piece. The tube is surrounded by a coil of wire which conducts the circuit current so that the electromagnetic field generated by the flow of current passes through both pole pieces. The stiffness of the spring and the viscosity of the liquid is chosen so that during normal current flow, there is little or practically no tendency for the movable pole piece to travel towards the end pole piece. An armature is located in close proximity to the end pole piece and is so coupled to the circuit breaker contacts that if the armature is attracted and moved to the pole piece, the contacts are opened and the circuit is interrupted. Under conditions of normal current flow, the pole pieces are physically separated and the magnetic flux through the end pole piece is insuflicient to attract the armature. If a short circuit occurs, the current surge through the coil produces an electromagnetic field of such magnitude that the flux through the end pole piece is sufilcient to attract the armature and open the circuit. The two circuit conditions thus far described, namely normal and short circuit, are the extreme conditions, the intermediate condition is the overloaded circuit. In the usual overloaded condition there is insuflicient flux passing through the end pole piece to attract the armature; however, there is an electromagnetic field of sufiicient intensity traversing the movable pole piece causing it to move gradually towards the stationary pole piece. When the movable one contacts the stationary pole piece, the reluctance of the magnetic circuit is considerably reduced thereby increasing the intenstiy of the magnetic flux through the pole pieces to such an extent that the armature is attracted to the end pole piece to open the circuit. It should be apparent that the tube and pole piece assembly acts as a time-delay device, permitting a continuous overload condition to exist for a predetermined time before interrupting the circuit. Thus, in the industry, the tube and pole piece assembly is known as a hydraulic-magnetic time delay tube.

In order to provide a magnetic pole piece on a thin walled non-magnetic tube it has been customary in the industry to attach an iron pole piece to an open end of the non-magnetic tube by brazing or silver soldering.

3,344,376 Patented Sept. 26, 1967 This method requires the use of a flux and high temperatures which result in oxidation and glassy residuals of flux which must be removed by washing, pickling, rinsing and drying operations in order to have a clean tube free of all particles which may after become loosened and jam the moving parts in the time delay tube after it has been hermetically sealed. Any flux remaining in the tube may also react chemically with hydraulic fluids or metal parts and in this manner render the tube useless. The silver solder is expensive, the brazing and subsequent cleaning operations are both slow and expensive, and the method is in many ways poorly suited for use in high production, mechanized and automatic, or semi-automatic, manufacturing processes.

The non-magnetic tube commonly used in the manufacture of time delay tubes, of the type described, has ordinarily been made by drawing from sheet metal in a manner similar to that used for making cartridge cases. This method results in a thin walled tube of the required accuracy and uniformity but it produces a tube with one end integrally closed. Formerly this closed end has been parted olf in a separate operation so that a pole piece of magnetic material might be silver soldered on to replace it. By this old method the brazed joint is the seal for that end of the tube and any faulty joints result in leaky tubes.

A tube and pole piece assembly proposed in United States Patent No. 3,037,800 to overcome the aforementioned disadvantages without employing brazing as the method of attaching the pole piece to the tube comprises utilizing a annular flange of magnetic material, such as iron, mounted around the base of the tube, the tube having wedged within it at the bottom a slug of magnetic material which is braced against the annular flange disposed outside the tube to complete the pole piece structure. The flange has an inside edge of smaller diameter than the outside diameter of the tube, such that when it is assembled on the tube containing the wedged slug, the edge bites into the surface of the tube against the slug without collapsing the wall of the tube. Thus, the annular flange is physically locked in position and together with the slug serves as the pole piece.

While the foregoing combination is a marked improvement over prior pole piece combinations, the use of the annular flange outside the tube tends to cause a spreading out of the magnetic flux at the bottom of the tube such that the full magnetic potential of the combination is not always realized.

It is an object of this invention to provide an improved tube and pole piece combination utilizing a pole piece assembled internally thereof having a configuration which makes it self-locating during assembly relative to the ele-' ments making up the tube.

Another object is to provide a tube and a pole piece combination wherein, during operation of the circuit breaker utilizing the same, the magnetic lines of force are concentrated at the bottom of the tube and not fringed outward as in prior combinations.

A further object is to provide a tube and pole piece combination which is structurally simple and easy to manufacture.

These and other objects will more clearly appear when taken in conjunction with the following disclosure and the accompanying drawings, wherein:

FIGURE 1 depicts one embodiment of a sealed tube and pole piece combination provided by the invention and shown partially in cross section;

FIGURE 2 is a cross section taken along line 2-2 of FIGURE 1;

FIGURE 3 shows the tube of the invention supported within a solenoid of a circuit breaker (not shown); and

FIGURE 4 shows diagrammatically relative to a portion of the tube and pole piece assembly the improved distribution of the magnetic lines of force during an operable portion of the circuit breaker cycle.

In its broad aspects the invention provides a hollow tubular member closed at its bottom end and having snugly seated within it a spherical ball of magnetic material, e.g. iron, having a diameter conforming substantially to the internal diameter of the tubular member. To insure wedging of the ball in position, the peripheral surface of the tube near its bottom has a plurality of dimples spaced on and around the tubular member, the distance of the dimples from the bottom end of the tube being greater than the radius of the magnetic spherical ball but less than its diameter, the dimples penetrating the surface of the tubular member sufiiciently inwardly thereof to grip said ball above its widest portion and hold it fast against the bottom of the tubular member. Preferably, the bottom of the tubular member should be spherically contoured to accommodate the ball; however, this is not necessary. By spacing and locating the dimples as stated above, the spherical ball is self-locating relative to the tubular member and mounting jigs are not necessary to the extent required in prior methods of manufacture.

Referring to FIGURE 1, there is depicted a sealed tubular member 1 partially broken away having a spherically contoured bottom 2 into which is tightly seated a spherical ball 3 wedged in place by dimples 4 (note FIGURE 2) penetrating inwardly of tubular member 1. The tube is sealed at the top by radially inwardly projecting end wall 5, which is deformed inwardly by means of a spinning tool against a seal of elastomeric material, e.g. Neoprene (polymerized chloroprene) as described in a copending application United States Ser. No. 320,312 filed Oct. 31, 1963. Within the tubular member is contained a movable cylindrical magnetic core 6 having a reduced portion 7 fitted within a spring 8 for retarding the movement of the movable pole piece towards fixed pole piece 3, the end 9 of spring 8 being supportably seated around the top of spherical ball 3. The tubular member contains a liquid 10 of suitable viscosity. The reduced portion 7 of the movable pole piece is preferably spherically concaved at its end 1 1 with a radius of curvature substantially matching that of ball 3 at the bottom of tube 1. This construction has the advantage of maximizing the distribution and concentration of magnetic flux passing through movable core 6 and fixed pole 3 as depicted by flux path 12 shown in FIGURE 4 when current passes through coil 12 surrounding tubular member 1 as shown in FIGURE 3. Referring to FIGURE 4, concaved end 11 of extension 7 of the movable core seats on and coincides with the spherical surface of ball 3. As will be apparent, movable core 6 is self-locating relative to ball 3 when it is magnetically excited.

The tubular member or tube is formed of a relatively soft non-magnetic metal, for example such as copper or brass, it being understood that other non-magnetic metals may be used. As stated hereinbefore, the tube is deep drawn from sheet metal in a manner similar to that used for making cartridge cases. This method results in a thin Walled tubing of required accuracy and uniformity. A tube size comprising one embodiment of the invention is one having a length of about 1.5 inches, an I.D. of about 0.174 to 0.176 inch, and an CD. of about 0.190 to 0.192 inch, the bottom of the tube being preferably spherically formed as shown in the drawings. The Neoprene seal is produced from a cord of filament of about 0.078 inch in diameter, the neck of the seal being compressed to a diameter ranging from about 0.031 to 0.047 inch and terminating on each side of the deformed end wall into sealing beads 14 and 15 as shown in FIGURE 1. The tube 1 may have a wall thickness of about 0.008 inch.

The movable core may have a major diameter at its enlarged end of about 0.169 to 0.170 inch and a minor diameter at its reduced portion of about 0.135 to 0.140 inch, the steel ball having a diameter of about 0.170 to 0.172 inch, almost that of the ID. of the tube. Thus, in stating that the diameter of the steel ball conforms substantially to the ID. of the tube, it is meant that the steel ball may have a diameter several thousandths less than that of the I.D., or it may be slightly larger, it being understood that the steel ball may be forced into the tube, since the metal of the tube is relatively soft. In deep drawing the tube with a spherically formed bottom, the bottom will usually have a thickness less than the wall thickness of the tube, for example less than 0.008 inch. This is preferred as it sets up less shielding resistance to the magnetic flux passing through the steel ball during operation of the circuit breaker.

After the tube has been formed by deep drawing, a pluraltiy of dimples are formed into the surface near the bottom of the tube by a dimpling tool. As stated above, the dimples 4 are spaced along a circle circumscribing the periphery of the tube (note FIGURES 2 and 4) located above the bottom of the tube by a distance greater than the radius of spherical pole piece 3 but less than the diameter thereof. The dimples may comprise one, two, three or more in number, the dimples preferably being made after steel ball 3 is inserted into the tube against its bottom, the dimples locking the steel ball in place. Thereafter, spring 8 is inserted into the tube followed by movable core 6. The tube is then filled with a liquid of suitable viscosity and the open end closed against a cord of Neoprene in accordance with the method described in the United States patent application Ser. No. 320,312 filed Oct. 31, 1963.

Summarizing the advantages of the invention, by using a spherical steel ball as the fixed pole within the tube, spring 8 is automatically located. Moreover, the ball is self-locating and overcomes the problem inherent in using a cylindrical slug which is difiicult to orient properly when inserted in the tube. Generally the slug would tilt when inserted, resulting in rejects. By using a ball and forming the end of the core with a spherical concavity, optimum surface contact with the steel ball is insured and hence full use of the magnetic flux by minimizing reluctance is utilized. Dimpling of the tube simplifies anchoring the steel ball in position.

While the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A tube and pole piece assembly comprising, a hollow tubular member of non-magnetic material closed at its bottom end, a spherical ball of magnetic material having a diameter conforming substantially to the internal diameter of the tube seated into the bottom end thereof, and inwardly penetrating dimple means on the surface of saidtubular member disposed around the periphery of said tubular member near the bottom end thereof, the distance of said dimple means from the bottom of said tubular member being greater than the radius of said spherical ball but less than its diameter, said dimple means penetrating the surface of the tubular member sufliciently to grip said ball and to hold it in place against the bottom of the tubular member.

2. A tube and pole piece assembly comprising, a hollow tubular member of the non-magnetic material closed at its bottom end, a spherical ball of magnetic material having a diameter conforming substantially to the internal diameter of and seated onto the bottom end of said tubular member, the bottom of said tube being spherically contoured to receive said ball, and inwardly penetrating dimple means on the surface of said'tubular member disposed around the periphery of said tubular member near the bottom end thereof, the distance of said dimple means from the bottom of said tubular member being greater than the radius of said spherical ball but less than its diameter, said dimple means penetrating the surface of the tubular member sufiiciently to grip said ball above its widest portion and to hold it in place against the bottom of the tubular member.

3. A sealed tube and pole piece assembly comprising, a hollow tubular member of non-magnetic material closed at its bottom end, a spherical ball of magnetic material having a diameter conforming substantially to the internal diameter of and seated into the bottom end of said tubular member, a cylindrical movable core carried by a spring and disposed within said tube, a liquid filling said tube and hermetically sealed therein, and a plurality of inwardly penetrating dimples on the surface of said tubular member spaced around the periphery of said tubular member near the bottom end thereof, the distance of said dimples from the bottom of said tubular member being greater than the radius of said spherical ball but less than its diameter, said dimples penetrating the surface of the tubular member sufliciently to grip said ball above its widest portion and to hold it in place against the bottom of the tubular member.

4. A sealed tube and pole piece assembly comprising, a hollow tubular member of non-magnetic material closed at its bottom end, a spherical ball of magnetic material having a diameter conforming substantially to the internal diameter of and seated into the bottom end of said tubular member the bottom of said tube being spherically contoured to receive said ball, a cylindrical movable core carried by a spring and disposed within said tube, a liquid filling said tube and hermetically sealed therein, one end of said cylindrical core being spherically concaved and having a radius of curvature similar to that of the ball, and a plurality of inwardly penetrating dimples on the surface of said tubular member spaced around the periphery of said tubular member near the bottom end thereof, the distance of said dimples from the bottom of said tubular member being greater than the radius of said spherical ball but less than its diameter, said dimples penetrating the surface of the tubular member sufiiciently to grip said ball above its Widest portion and to hold it in place against the bottom of the tubular member.

References Cited UNITED STATES PATENTS 1,552,375 9/1925 Ainsworth 335--240 2,849,201 8/1958 Schelgunov 85-82 X 3,281,740 10/1966 Riefler 335-255 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner. 

1. A TUBE AND POLE PIECE ASSEMBLY COMPRISING, A HOLLOW TUBULAR MEMBER OF NON-MAGNETIC MATERIAL CLOSED AT ITS BOTTOM END,A SPHERICAL BALL OF MAGNETIC MATERIAL HAVING A DIAMETER CONFORMING SUBSTANTIALLY TO THE INTERNAL DIAMETER OF THE TUBE SEATED INTO THE BOTTOM END THEREOF, AND INWARDLY PENETRATING DIMPLE MEANS ON THE SURFACE OF SAID TUBULAR MEMBER DISPOSED AROUND THE PERIPHERY OF SAID TUBULAR MEMBER NEAR THE BOTTOM END THEREOF, THE DISTANCE OF SAID DIMPLE MEANS FROM THE BOTTOM OF SAID TUBULAR MEMBER BEING GREATER THAN THE RADIUS OF SAID SPHERICAL BALL BUT LESS THAN ITS DIAMETER, SAID DIMPLE MEANS PENETRATING THE SURFACE OF THE TUBULAR MEMBER SUFFICIENTLY TO GRIP SAID BALL AND TO HOLD IT IN PLACE AGAINST THE BOTTOM OF THE TUBULAR MEMBER. 